Method for manufacturing building elements comprising substiantially wood waste and cement



We United States Patent 3.403.205 METHOD FOR MANUFACTURING BUILDING ELEMENTS COMPRISING SUBSTANTIALLY WOOD WASTE AND CEMENT Tor Axel Ingvar Ottenholm, Tingvallavagen 16C, Marsta, Sweden No Drawing. Continuation-impart of application Ser. No. 209,762, July 13, 1962. This application Jan. 25, 1966, Ser. No. 522,848 Claims priority, application Sweden, July 14, 1961, 7,341/ 61 4 Claims. (Cl. 264-109) This application is a continuation-in-part of my application Ser. No. 209,762, filed July 13, 1962, now abandoned.

This invention relates to a method for treating wood wastes to be used as filling material for the manufacture of building elements consisting essentially of wood wastes and cement.

There are, first and foremost, two problems, which have to be solved when using wood or wood waste in concrete elements.

Wood or wood waste consists of more or less carbohydrates, such as sugar and acids. These substances have a decomposition effect upon cement. Consequently, it is quite impossible to manufacture a durable concrete element containing wood or wood waste without first eliminating said decomposition effect. This problem has to be solved.

The second problem involved in using wood or wood waste in concrete elements is that wood and cement are materials widely separated from each other with regard to properties of materials, such as coefficient of expansion for instance. Such concrete elements, in which both the cement and the wood or wood waste are part of the loadbearing system, compared with concrete elements, in which only the cement is load-bearing, besides having less compressive strength, also all the disadvantages connected with essentially different mechanical properties of said materials.

Several attempts of different kinds have been made to solve the first of the above-mentioned problems by chemical pre-treatment of the wood or wood waste product. It has been tried to neutralize the injurious substances by admixture of chemicals such as calcium chloride, calcium hypochloride, water-glass and the like; Since, however, such a treatment does not affect the carbohydrates in any appreciable degree, it has been tried by different methods to destroy the injurious substances. However, these methods are time-consuming as well as expensive and must, in order to get a satisfactory result, require a continuous control of the percentage of these injurious substances. In spite of this continuous control it has been found that building elements manufactured according to these methods in time have been subjected to a certain decomposition damage and do age to such a degree that they have become useless.

Amongmany known methods the folio-wing can be mentioned:

In a known method essentially for the manufacture of wood wool slab and panels incorporating wood wool as part or whole of the core the cement, i.e. a common powdered, hydraulically settable material, is made plastic with aqueous medium such as water and hardens on drying. The purpose is to form a continuous coating of cement slurry upon the surface of the wood wool or like'vegetable material and subsequent moulding the resultant mixture of wood wool and cement slurry. In this method the only pre-treatment step is to wet the wood wool or like which is naturally retained on the surface thereof and t the load-bearing system in a concrete element.

Patented Sept. 24, 1968 In another known method for mjntnfacturingmncmie such mm name chigp ngs or shavings, as ling material contrary to above 'nown method atiention has been paid to above-mentioned problem connected with the injurious substances. It has in this hod been su csted to add to the organic fibrous material A ion of sulfate, particularly aluminium sulfate or othe; heavy metal sulfate and then add a ba:e such asli ilk, cement-milk or another basic liquid.

In this way a gel is produced and after that ordinary cement is added to the mixture. It is stated that the final mineralized fibres of the fibrous material when considered in transverse section shows a structure which will be subdivided in several zones or layers of different character. The outermost zone is formed by pure cement, then follows a layer in which cement is mixed with the hardened gel, further in there is a thin layer of hardened gel, then comes a zone in which the gel is mixed with or has penetrated into mineralized fibre portions, and finally the innermost portion of more or less impregnated fibre material. Hereby, it is stated, the fibre material is completely protected against decomposition. However, this method has several disadvantages. The method is time-consuming as well as expensive. Thmtl% centration and dosing of the solution of su .aie an cor- IMF? the process 0 im re nation. Incorrect dosingmmrfithtgrfiing on the fibres and may produce a dangerous sulfate containing insulating layer preventing linkage of the cement with fibrous material. Furthermore, the fibrous material becomes part of The method according to the invention for pre-treating of the wood waste is completely different from the abovernentic-ned methods and by the present method the aforesaid disadvantages are eliminated.

The present invention is based on the idea of achieving a firm film around the woo-d waste pieces with such characteristics that the pieces become encased in such an effective way that the injurious substances can not pierce the film and damage the cement in the concrete. Furthermore, the film is permanently effective to hinder the injurious substances from passing through after some time. Finally, the film is such that the cement in the cement mortar for the manufacturing of the concrete elements effectively binds on the film.

The method according to the invention for treating wood wastes to be used as filling material for the manufacture of building elements consisting essentially of wood wastes and cement comprises the steps of powdering onto and rubbing into thoroughly moistened pieces of wood waste cement clinker, that is, portland cement without the admixture of gypsum, wh reby the pieces of wood waste are rapidly encased, and drying the surface of the thus treated pieces of wood waste so that a firm film is formed around each of said wood waste pieces.

The present invention also relates to a method for manufacturing building elements consisting essentially of wood wastes and cement comprising the steps of powdering onto and rubbing into thoroughly moistened pieces of wood waste cement clinker, that is, portland cement without the admixture of gypsum, drying the surface of the thus treated pieces of wood waste so that a firm film is formed around each piece of said wood waste, mixing the dried, treated wood waste pieces with cement and water, whereby the cement in the water binds on the film on each piece of said wood waste, and thereafter molding the resulting mixture into a building element.

Since the initial material used, e.g. the wood waste pieces, is thoroughly moistened and the powdering and rubbing operation as well as the subsequent drying step affects only the surface, the interiors of the wood waste pieces have a high moisture content even after the powdering, rubbing and drying operation. As a result thereof,

when the building element is in its ready state and finally dry, it is given a high porosity; that is, the wood waste pieces will then shrink. It is, first and foremost due to this porosity that a building element having filling material pre treated according to the present invention has low density, low swelling and good heat and sound insulation. The wood waste pieces lie within the firm film as dried pips in a core. The shrinking continues by time and furthermore a certain decomposition of the wood waste pieces takes place. Thus, the porosity even increases in time.

A building element manufactured according to the present invention has furthermore the essential advantage over the, up till now, known methods, that only the concrete is load-bearing. The wood waste pieces, which at the pretreatment process are thoroughly moistened and they then have their largest volume, lie as mentioned above when the element is in its finished state as dried pips in a core. Thus the wood waste pieces are not part of the load-bearing system. Hereby, the problems associated with the different mechanical properties for different materials in the load-bearing system for a building element consisting of said different materials, such as modulus of elasticity, are eliminated. This also means a comparatively larger compressive strength for a building element manufactured according to the present invention.

The best result is obtained by employing only bark, in which case prior to the powdering and/or rubbing step the bark is preferably cut into pieces of between Va" and 2", preferably about 1". However, even through wood bark is the preferred wood waste material, other wood waste products from saw mills, for example knots, chips, etc. are also useful in the process of the instant invention.

The amount of bark to be used is preferably such, that the final product contains 30-70 percent by weight of dry bark, but it may even contain between and 90 percent by weight.

When being powdered and rubbed the wood waste or other wood waste material should have a moistness of about 35%. This moistness is obtained, for example, by maintaining the bark for a longer period in a water store and subjecting it thereafter to centrifuge treatment. However, wood bark or other wood waste material having a moisture content of between and 70% is also useful in the present invention.

For obtaining particularly good adhesion between the bark and the cement mortar, the film resulting from the powdering and/or rubbing step may be moistened outwardly after drying, thereafter the bark pieces are powdered again with cement clinker, that is, portland cement without the admixture of gypsum, and finally dried outwardly before the said pieces are mixed with the remaining components of the building element.

The moistening of the film obtained by the first powdering and/or rubbing step is preferably carried out such, that the bark is passed through a shower bath, that is, subjecting the bark to a slight water sprinkling.

Both the first and the second powdering or rubbing operation is preferably performed in such a manner, that the bark and the said cement without setting time control are rotated together in a slowly rotating drum whereby the cement is partially rubbed into the voids of the bark and thereby closes the same in an effective manner.

During moulding, the mixture is preferably subjected to a vigorous vibration, and at the same time may be subjected to a light pressure, for example in the order of 0.1 kg./cm. The building elements in connection therewith may be reinforced in the same manner as conventional concrete. After the moulding operation. is complete the building elements should after about two days be first removed from the moulds. Prior to their application, the elements must be stored in open air for at least 28 days, or for about 14 days in open air and for about 7 days in a drying chamber at a temperature of 20-40 C.

Due to the fact that' the bark used is thoroughly moistened, and that the glazing, i.e., the powdering and subsequent drying, affects only the bark surface, the interior of the bark has even after the glazing operation a very high moisture content. As a result thereof, when the building element in ready state is finally dried, it is given a high porosity, as the bark then will shrink. It is, among other things, due to this porosity that the finished building element has low density, low swelling and good heat and sound insulation. The advantage of using cement which has no controlled setting time lies in the fact, that this cement is setting rapidly when it is brought into contact with the moist bark surface. This results further in a highly effective encasing of the components comprised in the bark, for example sugar, which otherwise for example would deteriorate the adhesion between the bark and the cement mortar.

The less water that is used in the cement mortar, the stronger the finished building element will be. In a general operation, normally 160-170 litres of water are used per cm. mortar of cement. However, the amount of water must be of sufiicient volume to produce a liquid mortar.

Moreover, even the amount of cement in relation to the total amount of bark, sand, slag and the li-ke is an infiuencing factor on the strength of the finished building element. Further, the more cement that is added, the stronger the final product will be. But at the same time, the final product will thereby become more expensive and heavier. For this reason, a compromise appears preferable, for example 15% by weight of cement for slabs to be used as inner walls, and about 30% by weight for slabs intended for external walls.

A ready dried slab may have the following composition (irrespective of that it contains even a certain amount of water). The composition percentages given below are by weight of the individual constituents in the composition:

Cementl0-50%, preferably 15-30% Bark90-l0%, preferably -30% Sand-0-50%, preferably 15-30% Slag0-50%, preferably 0-30% The total percentage of the individual constituents of the composition must, of course, not exceed 100%. In this regard when, for example bark is used, no sand or slag can be added, because there must be a cement content of at least 10%.

In the following, it is briefly described by way of an example how a slab according to the invention may be manufactured by the method according to the present invention.

(1) Bark of fir and redwood is taken from a water store (even other bark types may, however, be used).

(2) The bark is washed clean from sand and clay.

(3) The bark is cut to pieces of between /2 and 1".

(4) The bark is subjected to centrifuge treatment until it contains about 35% water.

(5) The bark is rotated in a slowly rotating drum together with cement the setting time of which is not controlled.

(6) The bark is dried, for example by passing it on a belt through a heating and/or ventilating arrangement.

(7) The glazed bark is sprinkle-d with water, for example by passing the bark on the same belt as in point (6) through a shower arrangement.

(8) The bark is rotated in a slowly rotating drum together with cement the setting time of which is not controlled.

(9) The bark is dried, for example in the manner according to (6). v

(10) 40% by weight of the glazed bark with an inner moisture content of about 35% is mixed with 60% by weight of cement mortar made of cement, sand and/or granulated slag and water.

(11) The mass resulting thereof is moulded whilst vibrated vigorously.

(12) The slabs are taken out of the moulds after two days and, prior to their use, stored in open air f r about 30 days.

The invention is, however, not restricted to the above example, but may be varied within the scope of the accompanying claims. The manufacture of a slab requires, for example, not all of the aforesaid twelve steps in order to satisfy the requirements listed at the beginning of the description and to have a strength which by far exceeds that of usual lightweight concrete, but yet has a density below 1. For example, in many instances the steps 7-9 may be deleted. It is, furthermore, possible to exchange certain steps against equivalent ones. For example, the powdering must not be carried out in a rotary drum, but may, for instance, occur by means of pressure-spraying.

What I claim is:

l. A method for treating wood waste to be used as filling material for the manufacture of building elements consisting essentially of wood wastes and cement, which comprises the steps of powdering onto and rubbing into thoroughly moistened pieces of wood waste cement clinker (portland cement without the admixture of gypsum), whereby the pieces of wood waste are rapidly encased, and drying the surface of the thus treated pieces of wood waste so that a firm film is formed around each piece of said wood waste,

2. A process according to claim 1 wherein the firm film formed around the said pieces of wood waste is further moistened after the initial drying step, said moistened pieces of wood waste being subjected to a powdering and rubbing step with cement clinker, and thereafter drying the surfaces of said treated pieces of wood waste prior to being used as a filling material for the manufacture of building elements.

3. A method for manufacturing building elements consisting essentially of wood wastes and cement, which comprises the steps of powdering onto and rubbing into thoroughly moistened pieces of wood waste cement clinker (portland cement without the admixture of gypsum), drying the surface of the thus treated pieces of wood waste so that a firm film is formed around each piece of said wood waste, mixing the dried, treated wood waste pieces with cement and water, whereby the cement in the water binds on the film on each piece of said wood waste and thereafter molding the resulting mixture into a building element.

4. A process according to claim 3 wherein the firm film formed around each piece of said wood waste is further moistened after the initial drying step and subjected to a powdering and rubbing step with cement clinker, thereafter drying the surfaces of said treated pieces of wood waste prior to their use as a filling material for the manufacture of building elements.

References Cited UNITED STATES PATENTS 11/1923 Schumacher 10693 11/1931 Wilhelm 106108 3/1933 Respess 10693 5/1933 McMillan 10693 1/1951 Hansen 10693 9/ 1958 Comisso 10693 10/1959 Brunton 10693 FOREIGN PATENTS 3/1922 Great Britain, 11/1926 Great Britain.

ROBERT F. WHITE, Primary Examiner. T. I. CARVIS, Assistant Examiner. 

1. A METHOD FOR TREATING WOOD WASTE TO BE USED AS FILING MATERIAL FOR THE MANUFACTURING OF BUILDING ELEMENTS CONSISTING ESSENTIALLY OF WOOD WASTES AND CEMENT, WHICH COMPRISES THE STEPS OF POWDERING ONTO AND RUBBING INTO THOROUGHLY MOISTENED PIECES OF WOOD WASTE CEMENT CLINKER (PORTLAND CEMENT WITHOUT THE ADMIXTURE OF GYPSUM), WHEREBY THE PIECES OF WOOD WASTE ARE RAPIDLY ENCASED, AND DRYING THE SURFACE OF THE THUS TREATED PIECES OF WOOD WASTE SO THAT A FIRM FILM IS FORMED AROUND EACH PIECE OF SAID WOOD WASTE. 